1. Field of Invention
This invention relates generally to ultrasound systems for inspecting a material and more particularly to processing ultrasound image signals.
2. Description of Related Art
Ultrasonic sound waves are commonly used when it is desired to perform a non-destructive or non-invasive inspection of a material, such as an organic body tissue, for example. Ultrasound systems are generally configured for either industrial or medical inspections. However the underlying principles of operation of such devices remain substantially the same and a major differentiator between medical and industrial systems is the type of material being inspected.
Ultrasound systems are generally useful in providing a display of internal structural characteristics of a material or objects located within the material. In some medical ultrasound inspections it is desired to view a relative position of objects within an organic body material. Such objects may be more highly reflecting than most body tissues.
For example, in prostate brachytherapy, an ultrasound system with a transrectal ultrasound (TRUS) transducer may be used to image a needle and/or small radioactive seeds, which are introduced into the prostate through a bore of the needle. The radioactive seeds are generally cylindrical, are typically less than 5 mm in length, and have a diameter of about 0.5 mm to about 1 mm, such that they can pass through typical needle bores. The radioactive seeds may include a medically-suitable radioisotope, for example I-125 or Pd-103. Conventional brightness mode (B-mode) ultrasonography is generally accepted to be unreliable for displaying objects within the prostate tissue.
Several methods and specialized apparatus have been employed for seed detection in brachytherapy using ultrasound.
PCT Patent application WO2005/092197A1 by Fenster et al. discloses an apparatus for automated seed segmentation from three-dimensional (3D) B-mode TRUS images. However, the use of 3D images is unlikely to increase the contrast between the implanted seeds and the surroundings, when using B-mode signals to produce the images.
U.S. Pat. No. 6,549,802 to Thornton et al. discloses a localization system that combines X-Ray fluoroscopy together with B-mode TRUS ultrasonography for identifying the radioactive seeds. However an image combination and registration requirement between the X-ray and ultrasound images is likely to increase examination time and cost.
U.S. Pat. No. 6,245,016B1 to Daft et al. discloses a post-beamformer signal processing algorithm for improving ultrasound B-mode resolution and contrast. The algorithm is based on a model of the imaging process that represents a shape of the pulse transmitted by the transducer and the frequency-dependent attenuation of that pulse as it propagates through tissue and back to the transducer, the effects of changes in frequency-dependent attenuation, and changes in scatterer density as the pulse propagates across tissue boundaries and through cystic and calcified structures.
US Patent Application 2004/0039284A1 by Alam et al. discloses several methods for enhancing the image of brachytherapy seeds by processing ultrasound radio frequency (RF) signals. A first disclosed approach employs Doppler ultrasound in which the radioactive seeds are vibrated within the tissue by vibration-inducing equipment. A second disclosed approach involves correlating image signatures with a reference signature of the radioactive seed, and a third approach discloses the use of elastography (strain imaging) wherein at least two sequential RF images under different levels of external compression are used.
There remains a need for better methods and apparatus for the ultrasound inspection of materials and particularly for inspection of organic tissues.